1. Field of the Invention
The present invention relates to an automatic focus adjusting (hereinafter it is referred to also as “AF”) system which is so called auto focus adjusting system or auto focus system, and more particularly, this invention relates to an automatic focus adjusting system and a method for adjusting automatic focus capable of focus adjusting by focus adjusting scanning in that focus adjusting state of an object image is varied, an evaluating value of focus adjusting which is indicative of focus adjusting state as a criterion is sought from object image information corresponding to the object image, the focus adjusting state is varied continuously or intermittently and a plurality of the evaluating values are obtained such that a focus adjusting state is searched in which the evaluating value of focus adjusting is the most appropriate, and relates to camera which utilizes the system and the method, an image input device including image scanner and copying machine, and an image capturing apparatus including optical observing equipment having microscope, telescope, binoculars and endoscope.
2. Description of the Prior Art
Generally in digital cameras many of them perform an automatic focus adjusting (AF) operation in which focusing lens (focus lens) that contributes to focus adjusting among photographing optical system is driven, image information is taken by image capturing device, for example, such as CCD (charge coupled device) and the like, a high frequency component of the image information is selected as an evaluating value of focus adjusting, that is to say, as an “evaluating value for AF (auto focusing)”, and a focus driving range is scanned then the focus lens is reset at a position where the evaluating value for AF has a peak. Commonly this automatic focus adjusting (AF) method is called as CCDAF.
A most basic CCDAF operation is schematically shown in FIG. 10 and FIG. 11. In this CCDAF operation a scan starting point is set on an end point for infinity and it is moved to the end point regardless of a position where the focusing lens locates when a sweep for the focus adjusting operation for the automatic focus adjusting is started, that is to say an initial locating point, and the scan is performed till an end point for the adjusted position of nearest focus and peak position is searched to adjust focusing on the point. Curves in FIG. 10 and FIG. 11 are schematically depicted in a condition that evaluating values for AF detected in the scanning are plotted in the vertical axis. In this respect depending upon the structure of a lens driving system, an operation to remove an effect caused by a back lash of gears and the like may be required, however, descriptions about constitution and operation to remove this back lash are omitted in the following specification and drawings because this kind of operation is related to so many various kind of technology which are well known in the art.
As shown in FIG. 10 and FIG. 11 when the operation for automatic focus adjusting is ordered, a focusing lens is at the setout moved from an initial locating position (that is to say a stopping position of the focusing lens at the time point) Po to an end point for infinity, that is to say the focusing lens is once moved toward a direction in which the lens is set back in this case, to focus adjusted position for infinity Pi, as a scan starting point, then the focus adjusting operation is performed in the direction of setting ahead within a whole range of focus adjusting scanning from the focus adjusted position for infinity Pi to the adjusted position of nearest focus Pn. By this whole range scanning, peak position of the evaluating value for AF is detected as a focus adjusted position, in other words as a adjusted position of final focus Pe, then after the whole range scanning the focusing lens is set at the adjusted position of final focus Pe by a returning back operation toward the setting back direction and then the automatic focus adjusting is completed.
FIG. 10 shows a case when the initial locating point Po is located in a side of the end point for infinity in relation to a central position Pc of the lens movable range, and FIG. 11 shows a case when the initial locating point Po is located in a side of the adjusted position of nearest focus in relation to a central position Pc of the lens movable range.
In the devices depicted in FIG. 10 and FIG. 11 they spend so much useless time because they have comparatively many lens movements other than for actual focus adjusting scan such as the moving operation to the scan starting point, returning back operation to the focus adjusted position and the like. For example in the device shown in FIG. 11, because the operation is once returned to the end point for infinity Pi though the initial locating position Po is located at a position near to the adjusted position of nearest focus Pn, it is made to move across almost all the lens movable range.
On the other hand a method depicted in FIG. 12, FIG. 13 and FIG. 14 is arranged to move the focusing lens at the setout from the initial locating position Po to any “one end which is located nearer” selected from the end point for infinity and the end point for the adjusted position of nearest focus, and then scanning is begun from the nearer point. That is to say when the automatic focus adjusting is ordered, as shown in FIG. 12 to FIG. 14, one end point which is nearer to the initial locating position is selected from the end point for infinity Pi and the end point for the adjusted position of nearest focus Pn which are both ends of the lens movable range, is specified as a starting point of the scanning, and the focusing lens is moved to the specified end point at the setout, then the focus adjusting scan across the whole focus adjusting scan range is performed from the specified end point to the other end point. By this whole range scanning, the peak position of AF evaluation value is detected as the adjusted position of final focus Pe and the focusing lens is set at the adjusted position of final focus Pc by a returning back operation of the focusing lens after the whole range scanning then the automatic focus adjusting is completed.
FIG. 12 shows a case when the initial locating point Po is located in a side of the end point for infinity Pi in relation to the central position Pc of lens movable range, FIG. 13 shows a case when the initial locating point Po is located in a side of the end point for the adjusted position of nearest focus Pn in relation to the central position Pc of lens movable range, and FIG. 14 shows a case when the initial locating point Po is located in a side of the end point for the adjusted position of nearest focus Pn in relation to the central position Pc of lens movable range and especially FIG. 14 shows a case the adjusted position of final focus Pe is located between the initial locating point Po and the above mentioned the nearer end point. By a method of this kind time until the whole range scanning is begun, can be cut down.
However in a method depicted in FIG. 12 to FIG. 14, because the scanning direction in the method is changed according to the initial locating point Po, in a case when the evaluating value for AF has a “dependence of scanning direction”, a calibration equal to an amount of the dependence must be achieved. In fact it is usual that the evaluating value for AF has the dependence of scanning direction caused by the above mentioned back lash, a discrepancy of mechanical time constant because of difference in moving direction of the focusing lens and the like, an appropriate calibration for the dependence of scanning direction must be achieved by means of dependence of scanning direction data which were obtained through an experimental manufacturing stage.
Moreover it becomes an important factor that a shortening of the focus adjusting operation is cut down when speeding up of automatic focus adjusting operation is intended. That is to say, in the devices depicted in FIG. 10 and FIG. 11, and FIG. 12 to FIG. 14, it is not a moving operation from the initial locating position Po to the scan starting point and a returning operation to the final focus adjusted point Pe after the full range scanning but a time for whole range scanning in other wards, a time period which is required to perform whole range scanning across all area of the focus adjusting scan, that in fact occupies a major part of the time of automatic focus adjusting.
A number of data to be obtained by a scanning for focus adjusting operation is decided depending upon characteristics of a focusing lens and CCD as a image capturing element, and in usual case if a focusing motor which drives the focusing lens is a pulse motor, it is required to obtain one datum in every two or four pulses of the focusing motor. Usually a frequency of obtaining image information in the image capturing element and the like is about a level of one thirtieth ({fraction (1/30)}) second, because of this, it is required a driving whose every one pulse of focusing motor takes one sixtieth ({fraction (1/60)}) to one—one hundred twentieth ({fraction (1/120)}) second. That is to say data are obtained while the focusing motor is driven in a state of 60 to 120 pps (pulse per second) as a rate of pulse for the focusing motor.
On the other band because the moving operation to the scan starting point and a returning operation to the focus adjusted position are decided only by a mechanical constraint at the operating mechanism, they are usually driven in a state of 500 to 1000 pps as a rate of pulse. That is to say even when the same number of pulses are counted these two operations have time difference in level of about 4 to 17 times. By this reason it is more effective to be narrower for an area to be scanned to attain a cutting down of time for automatic focus adjusting required in automatic focus adjusting operation.
FIG. 15, FIG. 16 and FIG. 17 show other conventional method for automatic focus adjusting which is arranged under considering with the above described problems, it is a method to realize a speeding up by means of a sequence that “when a peak of evaluating value for AF is detected, the scanning is interrupted and the focusing lens is moved to the detected peak position.” In this method it is significantly important that “how is it judged that a peak of evaluating value for AF is detected?” That is to say it is not rare that a plurality of peaks of evaluating value for AF are generated because a plurality of object to be photographed can exist in different distance at a same time in actual using condition. In a situation where plurality of peak are generated in evaluating value for AF as above described, the peak must be detected with a strict judgment about an absolute value of evaluating value for AF at a peak, a relative value to other evaluating value for AF (evaluating value for AF for peripheral area, evaluating value for AF at other peak like portion and so on), further a tendency of gradient of evaluating value for AF around a peak and the like in order to match a focus adjusted position onto a peak that the operator is actually expecting.
For this purpose it is arranged that a judgment is made when the scanning has been continued for a moment around a certain area, even after a portion which seems to include a peak is passed in a process the focus adjusting scan as shown in FIG. 15 to FIG. 17. When a focus adjusting operation is ordered, one end which is located nearer to the initial locating position Po is selected as a scan starting point from the end point for infinity Pi or adjusted position of nearest focus Pn at the both ends of a lens movable range, and at the setout the focusing lens is moved to the scan starting point, then the focus adjusting scan is performed toward another end point as shown in FIG. 15 to FIG. 17. When a peak of evaluating value for AF is detected in a process of the focus adjusting scan, the peak is checked while the scanning is continued for a moment around a certain area, based on a result of checking, a peak position of evaluating value for AF is judged as a focus adjusted position in other words as a focus adjusted position Pe then the focus adjusting scan is stopped and the focusing lens is set on the focus adjusted position Pe by an moving back operation thereby the automatic focus adjusting operation is completed. FIG. 15 shows a case when the initial locating point Po is located in a side of the end point for infinity Pi in relation to the central position Pc of lens movable range, FIG. 16 shows a case when the initial locating point Po is located in a side of the end point for the adjusted position of nearest focus Pn in relation to the central position Pc of lens movable range, and FIG. 17 shows a case when the initial locating point Po is located in a side of the end point for the adjusted position of nearest focus Pn in relation to the central position Pc of lens movable range and a case the adjusted position of final focus Pe is located between the initial locating point Po and the above mentioned the nearer end point.
For a method of this kind, in many cases it is arrange in usual case to have a criterion of peak judgment which is considerably severely settled in order to minimize occurrence of failed focus adjusting, and when an ambiguous result is obtained, to perform the whole range scanning. However, because the scanning range can be significantly narrowed as depicted in FIG. 17 which corresponds to a case depicted in FIG. 14 when in a case the peak is detected, time for scanning is dramatically reduced, thereby speeding up of automatic focus adjusting operation ca be realized.
As for speeding up method other than above described “counter direction scanning” and “interruption of scanning when peak is detected”, a method can be thought that “immediately starting scan from the initial locating position Po” as disclosed in Japanese Patent Laid Open Publication No. Hei 05-241066. That is to say in Japanese Patent Laid Open No. Hei 05-241066, it is disclosed that in order to realize speeding up of automatic focus adjusting operation, focus adjusting scan is initiated from the initial locating position Po to an end point which is located nearer to the initial locating position Po and when any peak could not be found during the scan from the initial locating position Po to the nearer end point, then the focusing lens is moved back to the initial locating position Po and the focus adjusting operation is performed again this time toward the end point which is located farther. The concrete operation is depicted in FIG. 18, FIG. 19 and FIG. 20.
As shown in FIG. 18 to FIG. 20 when the operation for automatic focus adjusting is ordered, the first focus adjusting scan (depicted “scan 1”) is performed from the initial locating position Po as the scan beginning point toward the end point selected from focus adjusted position for infinity Pi and the adjusted position of nearest focus Pn which is locating nearer to the initial locating position Po, moreover the focusing lens is moved back to the original initial locating position Po and then the second focus adjusting operation (depicted “scan 2”) is performed from the initial locating position Po to the other end point which is locating farther from the initial locating position Po. By these scannings, peak position of the evaluating values for AF is detected as focus adjusted position in other words as the adjusted position of final focus Pe, then after the whole range scanning the focusing lens is set at the adjusted position of final focus Pe by a returning back operation thereby the automatic focus adjusting is completed
FIG. 18 shows a case when the initial locating point Po is located in a side of the end point for infinity Pi in relation to the central position Pc of lens movable range, FIG. 19 shows a case when the initial locating point Po is located in a side of the end point for the adjusted position of nearest focus Pn in relation to the central position Pc of lens movable range, and FIG. 20 shows a case when the initial locating point Po is located in a side of the end point for the adjusted position of nearest focus Pn in relation to the central position Pc of lens movable range and FIG. 20 shows a case the adjusted position of final focus Pe is located between the initial locating point Po and the above mentioned the nearer end point.
In the case depicted in FIG. 20 the automatic focus adjusting operation is ordered and at the time point the first focus adjusting operation (scan 1) is completed from the initial locating position Po as the scan starting point to the end point which is locating nearer to the initial locating position Po from the both end points of the focusing lens movable range, when the peak or evaluating value for AF is detected the peak position is detected as the adjusted position of final focus without performing the second focus adjusting operation (scan 2) thereby the focusing lens is set to the adjusted position of final focus Pe by the moving back operation and the automatic focus adjusting operation has been completed.
By this method disclosed in the Japanese Patent Laid Open No. Hei 05-241066, because the moving operation to the scan starting point is eliminated, the speed up of automatic focus adjusting operation can be attained by just that much. Because the method disclosed in the Japanese Patent Laid Open Publication No. Hei 05-241066 which is depicted in FIG. 18 to FIG. 20, is adapted to the method depicted in FIG. 12 to FIG. 14, the operation of “interruption of scanning when peak is detected” is not considered, but it goes without saying that the operation of “interruption of scanning when peak is detected” can be introduced thereby much speeding up of the automatic focus adjusting operation can be attained.
However there are some problems in the operation “focus adjusting operation is initiated from the initial locating position Po” depicted in FIG. 18 to FIG. 20 based on the Japanese Patent Laid Open Publication No. Hei 05-241066. That is to say in this method as shown in especially in FIG. 18 and FIG. 19 because in this method the focusing lens is moved back to the initial locating position Po after the first scan has been performed from the initial locating position Po to one end point, the one part of focus adjusting scan in the focus adjusting operation becomes discontinuous. Accordingly this method has a problem that “is there any adverse effect to performance characteristics by one part of the focus adjusting scan becomes discontinuous?”. In the matter of fact because the evaluating value for AF obtained time has a discrepancy at the discontinuing point of the focus adjusting scan, there is an anxiety that evaluating value for AF becomes also discontinuous, in addition because the directions of focus adjusting scan at the scan discontinued point are different, there is a possibility that the dependence of scanning direction may cause some adverse effect on the evaluating value for AF. In other words when the peak position and the scan discontinued point are almost located on the same position as shown in FIG. 21, there is a probability that accuracy for peak detection is decreased. To make matters worse not only overlapping between the sum discontinuing point and the initial locating position Po, but in many case the initial locating position Po also overlaps with the last focus adjusted position, because of this it has a problem that a discontinuity of focus adjusting scan occurs at a position which has the highest probability of focus adjusted position existence and thereby accuracy of peak detection is decreased in certain extent when the continuous photographing of the same object to be photographed is considered.
Further it can be thought that there is a high provability the focus adjusted position is located in the vicinity of the initial locating position Po when a continuous photographing of the same object to be photographed is considered, if a focus adjusted position which is located near to the initial locating position Po can be detected in the first scan (scan 1 depicted in FIG. 18 to FIG. 20), in high provability the second scan (scan 2 depicted in FIG. 18 to FIG. 20) need not to be performed. On the contrary, when the focus adjusting scan is initiated from the initial locating position PO, as shown in FIG. 22, for the object to be photographed which is locating in the vicinity of the initial locating position Po but which is apart from it in an opposite direction to the scanning direction, the object to be photographed is included inevitably in a range of the second scan (scan 2). The technology which is disclosed in the Japanese Patent Laid Open Publication No. Hei 05-241066 still has a kind of problem when it is thought from the above describe view point.
Still further in the technology which is disclosed in the Japanese Patent Laid Open Publication No. Hei 05-241066, undesirable situation is also caused by in a case when the initial locating position Po is located near to the end points of the scanning range. That is to say as shown in FIG. 23, an area of the first focus adjusting scan (scan 1) becomes too short, and because of this, even when a something like peak is located with in the scanning area, it is made too hard to discriminate the point as a peak. As a result of this fact, because the focus adjusting operation is moved inevitably to the second focus adjusting scan (scan 2), the effect of speeding up of automatic focus adjusting operation is lost and only decreasing of accuracy of focus adjusting operation caused by an existence of the scan discontinuous point, is remained. In other words a situation where only demerit is remaining, is introduced.
Accordingly when the above described situation is considered, typically the below described two points are required as problems to be solved.
(1) To achieve further speeding up with ensuring a high accuracy of focus adjusting operation in a ease when the same object to be photographed is continuously photographed. That is to say the high accuracy of focus adjusting operation is ensured by means that a vicinity of the initial locating position Po does not become the scan discontinuing point, and at the same time to realize a detection of focus adjusted position which has a high provability to be located near to the initial locating position Po at the first focus adjusting scan (scan 1) without fail.
(2) To maintain further high accuracy of focus adjusting by means of intending to make a focus adjusting sequence proper after a photographing around vicinity of the end point for infinity or the adjusted position of nearest focus. That is to say in a case when an enough strength of scan cannot be ensured to discriminate a peak position as the first focus adjusting scan (scan 1), it makes effective speeding up of automatic focus adjusting operation difficult. As a result of this fact, a structure in which a situation such as the above mentioned is avoided from a scanning sequence of the automatic focus adjusting operation.